I always use brass ball valves with PVC. Over the years I've found PVC ball valves to become hard to open and close after being installed for a while. Probably the biggest thing to realize when installing a brass threaded valve onto PVC threads is that it is easy to cross thread the valve onto the PVC. The brass threads will cut their own path into the much softer PVC threads.

Thank you for the responses. I e-mailed Apollo and asked why they, specifically, recommended not using plastic pipe with their metallic ball valves....... "it is poor practice and never recommended to use plastic pipe and fittings with metallic valves since thermal expansion, external forces or other situations can cause breakage or leaking at or near the joint"

Their response was "Most design codes recommend using similar piping and valve materials. For instance, stainless steel valves are generally used in stainless steel piping systems. It is not uncommon to use plastic piping with metallic valves, but this practice is not acceptable to most design codes. This is mainly due to the differences in pressure ratings and corrosion resistance."

So, the manufacturer says its not code to do this, but you guys say it is o.k.. I don't understand the divergence of their recommendation vs. the real world. Is it against code to do this, and more important, are there breakage problems.

... but this practice [of mixing materials] is not acceptable to most design codes."

So, the manufacturer says its not code to do this, but you guys say it is o.k.. I don't understand the divergence of their recommendation vs. the real world. Is it against code to do this, and more important, are there breakage problems.

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Even if it is bad practice, I think it is not specifically "against code" in the way you might be thinking. As I understand things, "design codes" are related to what is considered acceptable to engineers or to the people hiring them to do design and specification work, but "plumbing codes" are what the inspector has in his or her National Plumbing Code book.

"thermal expansion, external forces or other situations can cause breakage or leaking at or near the joint"
I've personally never had this happen in my 25+ years in the trade and I've used brass ball valves with PVC and CPVC male adapters almost all the time. I don't expect I'll change this "poor practice" anytime soon. It's interesting to see Apollo's response to this.